Go to
http://www.robarm.com/XCR_Accuracy.htm
Disclaimer:
Given that the website is from the company that made the XCR there most be a grain of salt. However, I find that this is pretty good (but not exact) comparison to my own groups with a magnified optic.
My Personal Reality with the XCR
Are you going to punch regular one ragged hole groups at 100 yards with an XCR. Sadly no, not right now (More on this later). With practice I have found from my own experience and my range buddies that one can get 1.5-2 inch groups at 100 meters with regularity with practice and American Eagle (AE) 62 grain rounds. I have shot MOA groups but only recently after much practice and generally using 69 grain match rounds.
In my own experience 62 grain and 69 grain bullets seems to shoot the best through my rifle. I have no experience with 77 grain .224 bullets so I cannot comment on them.
The reason I say it
"not right now" is that compared to the AR15 the XCR is still an infant. The AR15 was not known to be the accurate and generally reliable (when kept lubed and maintained) firearm most of us know that it is, when it first arrived. The AR15 like most firearms have an exponential development. From my brief knowledge and minimal research I obtained these findings. If I am incorrect please politely add your findings with the reference. I'm human and can make mistakes (like throwing flyers to destroy amazing groups). The AR15 only truly started to become the light recoil tack driver after years of development starting with the U.S. Marines and Army Marksmenship Unit (AMU). The Marines first demanded changes that led to the A2 design (better sights, heavier barrel, and faster rifling twist). The AMU added match grade barrels, free floated them, and improved the trigger lock time. Next the ammo improved bringing match grade .223 ammo with 69, 75, 77 and 80 grain match bullets. The first AR15/AR10 came around 1964-5 and has taken almost thirty to forty years (SR-25 came around 1992 which boasted most "common" features and the Mk12 which appeared in 2002) before it really began to live up to it's potential.
Given that the XCR came out around 2005-06. I will afford it the possibility and potential to become as accurate as the AR15/AR10. Only now are we seeing custom stainless steel barrels thanks to Alberta Tactical Rifle. It will take time before gunsmiths fully understand the inner workings of the XCR and how it can be tweaked towards perfection. I believe the XCR will have a similar but likely slower development as it's popularity grows since it is not a service rifle/carbine in the U.S. military inventory.
Currently, I find the XCR to have generally good accuracy that would make it acceptable as a patrol rifle/carbine. What is deemed acceptable can have a different meaning for different people however. For this I consider that the U.S. military considered that the rifle had to shoot 4 MOA to qualify. The rifle had to be 2 MOA and the ammo 2 MOA and supposedly that is why 4 MOA is acceptable for a service rifle. Just something to think about.
Is the XCR perfect? No. Is any firearm perfect? I think not.
If you cannot live without your black/green rifle/carbine not able to shoot MOA or sub-MOA groups, don't buy it (at least for now). If you want one that works all the time as long as you do your part (good ammo, good magazines, seat the magazine properly... etc.), why not try it out.
References:
Venola, Richard (2005). "What a Long Strange Trip It's Been". Book of the AR-15 1 (2): 6–18.
http://world.guns.ru/assault/as18-e.htm
http://en.wikipedia.org/wiki/M16_rifle
http://en.wikipedia.org/wiki/United_States_Navy_Mark_12_Mod_X_Special_Purpose_Rifle
http://en.wikipedia.org/wiki/Comparison_of_the_AK-47_and_M16